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CVE-2021-42785

31
FAUCET Score

CVE-2021-42785 is a critical buffer overflow vulnerability affecting TightVNC Viewer (tvnviewer.exe). A remote attacker can exploit this by sending a specially crafted FramebufferUpdate packet from a malicious VNC server, leading to arbitrary code execution on the client system. With a CVSS score of 9.8, this vulnerability is easily exploitable over the network with no user interaction required, allowing for complete compromise of confidentiality, integrity, and availability. Despite its high severity, there is currently no public exploit code available, no evidence of active exploitation, and minimal community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
<= 2.8.59CPE matchmatch criteria
cpe:2.3:a:tightvnc:tightvnc:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
2.27%
Probability of exploitation in next 30 days
EPSS Percentile
81.2%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0227 is in the 71st percentile among its peer group of 36,862 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

tightvnc.com / whatsnew.php
Release NotesVendor Advisory